The comment was to try:

my $status = undef;
[download]

I tried this, as well as:

undef $status;
[download]

and

$oContainer->{msNPAllowDialin} = undef;
[download]

None of these things change the current setting no matter what the current setting is. I can't seem to make the msNPAllowDialin function accept a value of undef in any of it's forms.
John